Thank you very much for investigating this. NOFPU seems to be a valid workaround indeed.

The problem does NOT appear in QuickBasic, where Horner's formula works perfectly, even when a0 is placed at the start of the formula. I always wrote my programs in QuickBasic and never had that problem. I had a computer running in Windows XP, but due to the fact that Microsoft did no longer support …

No, I did a typing error. I really used y = a0 + etc.

I have a problem when using QuickBASIC in DOSBOX. Consider a polynomial of the 4th degree in x. The coefficients are a0 = 9.123 a1 = 0.21 a2 = 0.12 a3 = 0.06 a4 = 0.05 and the value is, say, 0.1. The polynomial is written in the usual form y = a0 + a1*x + a2*x^2 + a3*x^3 + a4*x^4. However, in order …